02 sensors

ok quick history...i got a P0420 code. Advance Auto and Autozone both said to changed the 02 sensor before the cat. I didn't have money so i bought a Bosch universal and changed it out. Few miles later check engine light came on again not to mention gas mileage wasn't getting better. So then I borrowed some money from a friend and went online to get an OEM sensor to change it out again. Then today I found out that bank 1 is actually the sensor AFTER the cat...(i want to cuss out the people at autozone and advance) now the question is...can i use the universal upstream sensor to replace to downstream just until i have money to get a OEM one? or is that like a really bad idea?

you know ive swapped them before but who knows you know ive got issues with them now too, but its been two years since ive swapped mine around, i believe they are the same part number though

i went ahead and did it. no problems so far so i hope it stays that way. planning on getting an OEM downstream in there asap. thanks!